Low Frequency notification appliances provide a life-saving value to sleeping occupants. Through NFPA funded research, it has been found that the 520 Hz square wave signal is the most effective at waking sleeping occupants. Six different signals were tested, and the 520 Hz had the highest waking rate of 92 percent. Since 2010 low frequency 520 Hz appliances have been fully adopted into the NFPA requirements. The compliance date for the requirement of low-frequency devices was set to January 1, 2014, giving the industry a five-year window to develop product standards.
Requirements that took effect January 1, 2014 state that audible fire alarm signals within sleeping spaces with the purpose of awaking occupants must be low frequency. Such as hotels, dormitories, multi-family residents but not hospitals or nursing homes because the communication system is meant to alert the staff which then notifies patients. Household fire alarms have also adopted the 520 Hz frequency.